Yes, it's okay to delete those files. MobileSheets replaces the existing xml file in two steps - it first writes the file to the temporary name, then replaces the existing file with that temporary file. It's handled this way in case MobileSheets is terminated unexpectedly in the middle of writing out the filters, as the filters file would be corrupted in that case. So it sounds like this scenario happened many times on your device... The other possibility is that MobileSheets created the temporary file, but could not delete and replace the existing file. In this scenario, there may be a bug as MobileSheets is not deleting the temporary file that was created.
Mike
Mike